MXPA06004573A

MXPA06004573A - Adaptive radio resource management for wireless local area networks.

Info

Publication number: MXPA06004573A
Application number: MXPA06004573A
Authority: MX
Inventors: Shamin Akbar Rahman
Original assignee: Interdigital Tech Corp
Priority date: 2003-10-31
Filing date: 2004-10-14
Publication date: 2006-06-27
Also published as: TW200623726A; NO20062237L; EP1683377A2; US20050094607A1; TW200947962A; CA2545489A1; KR20060096503A; TW200518505A; DE602004015139D1; TWI248731B; US20060277450A1; US7085228B2; EP1959613A1; EP1959613B1; WO2005046105A2; JP2007510365A; ATE465575T1; WO2005046105A3; DE602004026794D1; EP1683377A4

Abstract

In a wireless communication system including an access point and at least one wireless transmit/receive unit (WTRU), a method for adaptive radio resource management begins by examining a frame error rate value of a WTRU. Then, a channel utilization value of the WTRU and a current data rate of the WTRU are examined. System parameters for the WTRU are adjusted based on the examined variables.

Description

METHOD FOR ADAPTABLE MANAGEMENT OF RADIO RESOURCES IN A WIRELESS LAN FIELD OF THE INVENTION The present invention relates to the management of radio resources in wireless local area networks (LANs), and more particularly, to a method for adaptively managing radio resources in a wireless LAN.

BACKGROUND Wireless communication systems are well known in the art. Generally, said systems comprise communication stations, which transmit and receive wireless communication signals between one and the other. According to the type of system, the communication stations are typically one of two types: base stations or wireless transmission / reception units (WTRUs), which include mobile units. The term WTRU, as used herein, includes, but is not limited to, a user equipment, a mobile station, a mobile subscriber unit or fixed, a locator, or any other type of device capable of operating in a wireless environment. WTRUs include personal communication devices, such as telephones, video phones, and Internet ready telephones that have network connections. In addition, the WTRUs include portable personal computing devices, such as PDAs and notebooks with wireless modems that have similar network capabilities. Reference is made to WTRÜs that are portable or may otherwise change location as mobile units. The term "access point", as used herein, includes, but is not limited to, a base station, a Node B, a site controller, an access point, or any other interface device in a wireless environment that provides WTRU with wireless access to a network associated with the base station. Typically, a network of base stations is provided such that each base station is capable of establishing concurrent wireless communications with appropriately configured WTRs. Some WTRUs are configured to establish wireless communications directly between one another, that is, without being retransmitted through a network by means of a base station. This is commonly called wireless peer-to-peer communications. The WTRÜs can be configured for use in multiple networks with peer-to-peer and network communication capabilities. A type of wireless system, called a wireless local area network (LAN), can be configured to establish wireless communications with WTRUs equipped with WLAN modems that are also capable of establishing peer-to-peer communications with similarly equipped WTRUs. Currently, WLAN modems are integrated into a large number of traditional computing and communication devices by manufacturers. For example, cell phones, personal digital assistants, and laptops are built with one or more WLAN modems. A popular wireless local area network environment with one or more WLAN access points (APs) is built according to one of the IEEE 802.11 standards. The basic service set '(BSS) is the building block of an IEEE 802.11 LAN and consists of WTRUs referred to as stations. The set of stations that can talk to each other can form a BSS. Multiple BSSs are interconnected through an architectural component, called a distribution system (DS), to form an extended service set (ESS). An access point (AP) is a station that provides access to the DS through the provision of services DS and generally allows concurrent access to the DS through multiple stations. The 802.11 standards allow multiple transmission speeds (and dynamic switching between speeds) to be used to optimize performance. Lower transmission speeds have more robust modulation characteristics that allow greater range and / or better operation in noisy environments than higher transmission rates, which provides better performance. It is an optimization challenge to always select the best (highest) speed possible for any coverage and interference condition. The transmission speeds currently specified for several versions of the 802.11 standard are as follows: Conventionally, each 802.11 device has an implemented speed control algorithm, which is controlled only by that device. Specifically, the uplink speed control (UL) is carried out in stations and the downlink speed control (DL) is carried out in APs. The algorithm for switching speed is not specified by the standards. This is left to the criterion of the station and implementation of ??. These speed control algorithms are usually private and thus, public information about them is limited. However, several algorithms have been described in the industrial and academic literature. Generally, they are relatively simple algorithms based on the detection of lost confirmations (ACKs) and other statistics. The 802.11 standard specifies a common medium access control (MAC) layer, which provides a variety of functions that support the operation of wireless LANs based on 802.11. In general, the MAC layer manages and maintains communications between stations and APs by coordinating access to a shared radio channel and by using protocols that improve communications in a wireless medium. The MAC layer uses a physical layer (PHY), as defined in 802.11b or 802.11a, to carry out the tasks of carrier disposition, transmission, and reception of data frames. In general, each transmitted MAC layer data frame is confirmed by the receiver. Classically, this is referred to as the automatic stop request (ARQ) protocol "stop and wait" ("stop and walt"). If an ACK is not received by the transmitter (lost or never sent), then the original data box is considered lost and the transmitter will go through the containment procedure one more time and try to resend the data box. A lost ACK assumes that the receiver does not receive ACK at all. However, a check can be made to determine if an ACK frame can be partially lost (for example, the CRC of the load is bad, but the header information is intact). This can then be used in the decision procedure as an average condition between a lost ACK and a received ACK. An example of speed control algorithm based on performance is as follows. First, 10% of the data is sent periodically at two data rates adjacent to the actual data rate. Then, the performance at each of the three data rates is evaluated periodically considering the amount of data that is successfully confirmed with respect to the amount of data transmitted at a given rate. Finally, a switch is made to the data rate with the best performance. These algorithms are one-dimensional in form that only consider their own link quality (for lost ACKs) during a given transmission. Unlike a typical station, APs generally have knowledge of the total system and can, accordingly, consider more dimensions. For example, an AP can consider the UL data frame rate that was used by a given station within a given time window (for example, the previous X seconds) as the starting point speed for its DL speed transmission to said station. An AP can also track the last speed transmitted in the DL to a given station in the AP for a given period of time. Sometimes, it is better to transmit at higher speeds to all stations (even with a relatively high error rate), since transmitting a low data rate to a user tends to slow down the entire system. The switching and performance points (for example, the amount of error rate that a typical station application can tolerate) of this type of system can be characterized and used in the AP speed control. A finite-state machine (FSM) -based approach can also be applied (such as by radio resource management (RRM) double time division (TDD) 3GPP), where speed control can perform different actions for different cell states (loads). The cell state can be established, for example, by a congestion control algorithm. In addition, a wireless link can suffer a high frame error rate (FER) compared to a cable link. High FER can occur due to a high traffic load, which causes more collisions and consequently, a high FER; a bad wireless link condition, which may be due to high interference, fading, or the movement of a user away from an AP; or other reasons. The proposed RRM procedure manages adaptively the radio resources acting differently according to the reason that causes the high FER. If the high FER is due to a high traffic load, the RRM will try to reduce or regulate the traffic load, by activating traffic shaping functions or congestion control. If the high FER is due to a bad wireless link, the RRM attempts to increase the strength of the wireless link using a more robust modulation scheme. In a wireless communication system that includes an access point and at least one unit. wireless transmission / reception (WTRU), a method for Adaptive radio resource management is initiated by examining a frame error rate value of a TRU. Then, a channel utilization value of the WTRU and an actual data rate of the WTRU are examined. System parameters for the WTRU are adjusted based on variables examined. In a wireless communication system that includes an access point and at least one wireless transmit / receive unit (WTRU), a method for performing speed control is initiated by determining whether a downlink transmission has been performed on the WTRU within a predetermined previous time period. If a downlink transmission has been made, then the previous data rate is used as the initial data rate. If no downlink transmission has been made, then an initial data rate used before the predetermined time is selected. An apparatus for performing radio resource management (RRM) in a wireless communication system includes a measuring device, a RRM decision device, and at least one RRM action device. The measuring device is used to collect measurements in a wireless communication system and to calculate one or more metrics based on the measurements. He RRM decision device is used to evaluate each metric against a predetermined threshold. Each RRM action device performs a unique RRM function and is driven by the RRM decision device. An integrated circuit for performing radio resource management (RRM) in a wireless communication system includes a measuring device, a RRM decision device, and at least one RRM action device. The measuring device is used to collect measurements in the wireless communication system and to calculate one or more metrics based on the measurements. The RRM decision device is used to evaluate each metric against a predetermined threshold. Each RRM action device performs a unique RRM function and is driven by the RRM decision device.

BRIEF DESCRIPTION OF THE DRAWINGS A more detailed understanding of the invention can be obtained from the following description of a preferred embodiment, given as an example and to be interpreted together with the accompanying drawings, wherein: Figure 1 is a flow chart of a process for managing radio resources according with one embodiment of the present invention; Figure 2 is a flow diagram of a method in an AP according to an embodiment of the present invention; Figure 3 is a graph of a performance curve used by the speed control procedure shown in Figure 2; Figure 4 is a flow diagram of a lost ACK function used by the speed control procedure shown in Figure 2; and Figure 5 is a diagram of an apparatus constructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES As shown in Figure 1, an adaptive radio resource management (RRM) procedure 100 is invoked either periodically or against the detection of a high FER (FER_HIGH, which is a specific implementation value). The procedure 100 is started by comparing the measured FER value with the high FER threshold (FER_HIGH, step 102). If the measured FER value exceeds the FER_HIGH, then a comparison is made to determine if the channel utilization is greater than a high channel utilization threshold (CH_UTIL_HIGH; 104). If the channel utilization exceeds the CHJJTIL-HIGH, then the congestion control is operated (step 106) and the procedure is completed (step 108). The goal of congestion control is to reduce the traffic load and channel usage. In the control of congestion, the ?? You can disassociate 'stations that have one or more of the following characteristics: a high error rate, a low priority MAC address, an excessive channel utilization. From a programming perspective, the AP can retain a clear signal to send (CTS) for uplink transmission. In general, the station sends a send request (RTS) to an AP if the RTS / CTS mechanism is enabled in the BSS. If the AP retains the CTS, the station can not transmit packets on the uplink, thus relieving the congestion situation. For a user who frequently retransmits, their transmission speed can be reduced when there is congestion, which reduces the possibilities of containment / collision. If the channel utilization is less than the CH_UTIL_HIGH (step 104), then a determination is made as to whether the channel utilization is less than a low channel utilization threshold (CH_UTIL_LO; step 110). If the use of the channel is less than the CH_UTIL_LOW, then the actual data rate is examined to determine if it is greater than the minimum data rate (step 112). If the actual data rate is greater than the minimum data rate, then the speed control is operated to decrease the data rate (step 114) and the procedure ends (step 108). The speed control is carried out to reduce the data rate to adapt to the traffic load offered. When a ?? it does not use all the bandwidth and experiences a high error rate, its transmission speed can be reduced to increase the transmission quality. With a lower data rate, a more robust modulation scheme can be used, which improves the FER value in time. If the actual data rate is equal to the minimum data rate (step 112), then the traffic shaping is used to reduce the FER value (step 116), and the procedure ends (step 108). During traffic shaping, excessive data may be delayed to control traffic within the distributed bandwidth, and / or additional bandwidth may be allocated for high priority data. If the channel utilization exceeds CH_TITIL_LOW (step 110), then the traffic shaping is triggered (step 116) and the procedure is completed (step 108).

If the measured FER value does not exceed the FER_HIGH (step 102), then the measured FER value is compared to a FER threshold ba or (FER_LOW, step 120). If the measured FER value is less than the FER_L0, then a comparison is made to determine if the channel utilization is greater than the CH_UTIL_HIGH (step 122). If the channel utilization exceeds CH_UTIL_HIGH, then the actual data rate is examined to determine if it is less than the maximum data rate (step 124). If the actual data rate is less than the maximum data rate, then a speed control is operated to increase the data rate (step 126) and the procedure ends (step 108). By increasing the data rate, channel utilization will decrease. If the actual data rate is already equal to the maximum data rate (step 124) or if the channel utilization does not exceed the CH_UTIL_HIGH (step 122), then no further adjustments are made and the procedure is completed (step 108). If the measured FER is greater than the FER_L0W (step 120), then a comparison is made to determine if the channel utilization is greater than the CH_UTIL_HIGH (step 128). If the channel utilization exceeds CH_UTIL_HIGH, then a congestion control (step 106) is triggered and the procedure ends (step 108). If the channel utilization is less than the CH__UTIL_HIGH (step 128), then the channel utilization is compared with the CH_UTIL_LO (step 130). If the channel utilization is less than CH_UTIL_LOW, then the actual data rate is examined to determine if it is greater than the minimum data rate (step 132). If the actual data rate is greater than the minimum data rate, then a speed control is operated to decrease the data rate (step 114) and the procedure ends (step 108). If the actual data rate is equal to the minimum data rate (step 132) or if the channel utilization is greater than the CH_UTIL_ LOW (step 130), then no further adjustments are made and the procedure is completed (step 108). If the speed control is operated in step 114 or step 126, any applicable speed control procedure may be executed; Method 100 does not require the use of any particular speed control procedure. If so desired, method 100 may use a method 200 for speed control. In one embodiment of the present invention, a method 200, as shown in Fig. 2, is used for speed control in the. He procedure 200 is initiated by determining whether a downlink (DL) transmission was made to a specific station within the last X seconds (step 202). If no transmission was made within the last X seconds, then the initial data rate is determined from the following way. A check is made as to whether the last transmission speed for the station is available (step 204). If the last transmission speed to the station is available, then it is considered (step 206). If the last transmission speed for the station is not available (step 204), then a check is made as to whether the last received speed for the station is available (step 208). If the last received speed is available, then it is considered (step 210). If the last received speed is not available (step 208), then the last data rate transmitted from any other station is considered (step 212). Regardless of the initial data rate that is considered (from step 206, 210, or 212), the cell load is then verified (step 241). The cell load statistics are stored in the AP, and it is. the average channel utilization within the last Y seconds. The cell load is then evaluated (step 216). In the case of low traffic demand, the initial data rate is set for the last data rate considered in step 206, 210, or 212 (step 218). In the case of high traffic demand (step 216), the speed of determined using a performance curve, similar to that shown in Figure 3 ~ (step 220). These curves can be based on experimental results or can be updated dynamically and stored in a database, as explained below. The performance curves shown in Figure 3 are preferably stored in memory in the AP. The curves are based on statistics collected during the operation of AP. The x axis represents the channel utilization, which is the actual channel utilization plus the data rate for the next transmission. The y axis represents performance. Each curve corresponds to a certain FER interval, with provision of channel performance as a function of channel utilization and frame error rate. The procedure selects the data rate that provides the maximum performance for the current FER. Once the initial data rate is selected, the data frame is transmitted (step 222) and the AP waits for an ACK for the frame (step 224). After receive an ACK or when the ACK waiting period ends, the lost ACK count is updated (step 226) and the performance curve is updated (step 228). The procedure then returns to step 202. Speed control is a frame-based procedure; the loop presented by the return to step 202 represents the continuous transmission of frames. If there was a downlink transmission effected to a specific station within the last X seconds (step 202), then the lost ACK count is verified (step 230). The cell load is then verified (step 232) and evaluated (step 234). If the traffic demand is low, a lost ACK function is invoked (step 236), which is described in detail below. In the case of high traffic demand, the initial data rate is determined using a performance curve (step 238), similar to that used in step 220. Once the transmission data rate is selected, the data box is transmitted (step 222) and the AP waits for an ACK for the frame (step 224). After receiving an ACK or waiting for the ACK timeout, the lost ACK count is updated (step 226) and the performance curve is updated (step 228). The procedure then returns to step 202. The lost ACK function 40G (from step 236) is shown in Fig. 4. Function 400 is started by calculating the FER for a given period (step 402). The function 400 distinguishes whether the table is lost, partially lost (for example, the CRC of the load is bad, but the header information is intact), or received in error. Function 400 reacts more quickly when frames are lost than when they are partially lost or received in error. The difference in how much of the frame is lost can be used to determine how to adjust the speed control. For example, the speed will decrease less abruptly if there is a partially lost picture instead of a completely lost picture. The actual data rate is then recovered (step 404). A check is made as to whether the actual data rate is less than or equal to the maximum data rate and whether the FER value is low (step 406). If both conditions are met, then the channel is polled at the next data rate for a predetermined number of frames (step 408). In one embodiment of the present invention, the channel is polled during at least one frame. If all frames sent at a higher data rate are confirmed (step 410), then the AP switches to the next higher data rate (step 412), and the function ends (step 414). If all frames sent at the highest data rate are not confirmed (step 410), then no change is made to the data rate (step 416) and the function ends (step 414). If the tests of step 406 are not successful, then a further evaluation is performed to determine if the actual data rate is greater than the minimum data rate and the FER value is high (step 418). If both conditions are met, then the AP switches to the next lowest data rate (step 420) and the function ends (step 414). If these conditions are not met (step 418), then no change is made to the data rate (step 416) and the function ends (step 414). Figure 5 is a diagram of an adaptive RRM apparatus 500 constructed in accordance with the present invention; in a preferred embodiment, the apparatus 500 resides in a ??. The apparatus 500 includes a measurement module (or device) 510, a decision module RRM 530, and at least one action module 540. The measurement module 510 collects hardware measurements through a measurement accumulation module (or device) 512 and calculates performance metrics. The performance metrics calculated by the module 510 include FER 514, cell load 516, channel utilization 518, and lost ACK count 520. Additional metrics can be calculated by the measurement module 510 based on collected measurements. The decision module RRM 530 decides which action module to call based on performance metrics and predetermined thresholds, as explained above with reference to figure 1. The action modules 540 perform the specific RRM actions, and include a traffic forming module 542, a speed control module 544, and a congestion control module 546. Additional 540 action modules can be provided to perform additional RRM functions. It should be noted that while the present invention, for simplicity, has been described in the context of a wireless LAN type technology, the present invention can be implemented in any type of wireless communication system. Simply by way of example, the present invention can be implemented in a wireless LAN, UMTS-FDD, UMTS-TDD, D-SCDMA, CDMA, CDMA2000 (EV-DO and EV-DV), or any other type of wireless communication system . Although the features and elements of the present invention are described in the preferred embodiments. in particular combinations, each feature or element may be used alone (without the other features and elements of the preferred embodiments) or in various combinations, with or without other features and elements of the present invention. While embodiments of the present invention have been shown and described, a large number of modifications and variations could be made by one skilled in the art without departing from the scope of the invention. The above description serves to illustrate and not limit the present invention in any aspect.

Claims

1. Method for managing adaptive radio resources in a wireless communication system, system that includes an access point and at least one wireless transmission / reception unit (TRU), the method comprises the steps of: examining an error rate value of a WTRU box; examine a channel utilization value of the WTRU; examine an actual data rate of the WTRU; and adjust system parameters for the WTRU based on the variables examined.

2. Method according to claim 1, wherein the wireless communication system is an 802.11 wireless local area network, the access point is an 802.11 access point, and the WTRU is an 802.11 station.

3. Method according to claim 1, wherein the adjustment step includes performing speed control.

4. Method according to claim 3, wherein the step of performing speed control includes the steps of: determining whether a downlink transmission has been performed to the WTRU within a period of WTRU; previous predetermined time; if a downlink transmission has been made, then use the previous data rate as an initial data rate; and if no downlink transmission has been performed, then select an initial data rate used before the predetermined time period.

5. Method according to claim 4, wherein the selection step includes selecting the first data rate available between: the last data rate transmitted to the TRU; the last data rate received in the WTRU; and the last data rate transmitted to any WTRU in the system.

6. Method according to claim 4, further comprising the steps of: evaluating the cell load; and adjust the initial data rate based on the traffic demand in the cell.

7. Method according to claim 1, wherein the adjustment step includes performing congestion control.

8. Method according to claim 1, wherein the adjustment step includes effecting formed traffic.

9. A method for carrying out speed control in a wireless communication system, which includes an access point and at least one wireless transmission / reception unit (WTRU), the method comprises the steps of: determining if. a downlink transmission to the WTRU has been effected within a predetermined prior period of time; if a downlink transmission has been made, then use the previous data rate as an initial data rate; and if no downlink transmission has been performed, then select an initial data rate of at least one data rate, used before the predetermined time period.

10. Method according to claim 9, wherein the selection step includes selecting the first available data rate between: the last data rate transmitted to the 'WTRU; the last data rate received in the WTRU; and the last data rate transmitted to any WTRU in the syste

11. Method according to claim 9, further comprising the steps of: evaluating the cell load; and adjust the initial data rate based on the traffic demand in the cell.

12. Method according to claim 9, wherein the wireless communication system is an 802.11 wireless local area network, the access point is an 802.11 access point, and the WTRU is an 802.11 station.

13. Apparatus for carrying out radio resource management (RRM) in a wireless communication system, comprising: a measuring device, for collecting measurements in the wireless communication system and for calculating one or more metrics based on the measurements; an RRM decision device, for evaluating each one, of one or more metrics with respect to a predetermined threshold; at least one RRM action device, and each RRM action device performs a unique RRM function and is driven by said RRM decision device.

14. Apparatus according to claim 13, wherein the wireless communication system is a network 802.11 wireless local area (WLAN) and said device is located at an access point on the WLAN.

15. Apparatus according to the. Claim 13, wherein each of one or more metrics is selected from the group comprised of: frame error rate, cell load, channel utilization, and lost confirmation count.

16. Apparatus according to claim 13, wherein each of at least one of the RRM action devices is selected from the group comprised of: formed of traffic, speed control, and congestion control.

17. Integrated circuit for carrying out radio resource management (RRM) in a wireless communication system, comprising: a measuring device, for collecting measurements in the wireless communication system and for calculating one or more metrics based on the measurements; an RRM decision device, for evaluating each of one or more metrics with respect to a predetermined threshold; At least one RRM action device, and each RRM action device performs a unique RRM function and is driven by the device.

RRM decision. 18. Integrated circuit according to claim 17, wherein the wireless communication system is a wireless local area network (LAN) 802.11 and said integrated circuit is located at an access point in the WLAN.

19. Integrated circuit according to claim 17, wherein each of one or more metrics is selected from the group comprised of: frame error rate, cell load, channel utilization, and lost confirmation count.

20. Integrated circuit according to claim 17, wherein each of at least one of the RRM action devices is selected from the group comprised of: formed of traffic, speed control and congestion control.